350 motor build
 

I was thinking of building A motor for my boat this winter. I have a 260hp mercruiser now. I was going to get a used block send it to the machine shop have it cleaned. I was thinking of a set of vortech 64cc heads an a edelbrock performer intake. My question is what cam to use? I also think I'll use d dish pistons. An will my Qjet carb feed this motor. I believe it's a 750cfm.

Lots of cam choices. Not sure what year motor but if you can I recommend a hyd. roller set up. Comp Cams, Crower and RM builder all have good options. Need more specifics on what you want to do and your parts list to get more specific on cam choices.

Im going to stick with a flat tappit cam. I'm doing a budget build. So let's say I stick with a stock bottom end an put a set of vortech head with a performer rpm intake. I'm looking for around 350-375hp. I know it's easy to do with this setup.

IMO the difference in cost between roller and flat tappet is not that much considering the benefits, remember there is little to no zinc in standard engine oils. To run a flat tappet you need to run motorcycle oil which has zinc along with quite a cost difference. When a FT starts to go it sends bits of metal through the entire engine, it is rare to have a roller do similar damage.

That's why I run rotella T synthetic in my motor now. This motor I have now has 720hrs on it an all I've ever done was change oil An had the valve springs changed a years had 2 sunken seat on a set of valves. Other then that bore still had cross hatches an the lifter still had a little cave to the they weren't quite flat yet.

Trash is right we need more info. like what you want to do, what kind of boat is it? How's your exhaust system, and which style do you run and are you willing to buy aftermarket to achieve your goal, also a BIG one is how much $$$ can you afford, it all really boils down to that, because things aren't cheap. I've got a motor in my small boat 18.6' Chris Craft Scorpion that has a 260 in it. I modifiied it cheap and it runs like a scalded dog. It came with through hull exhaust, here's what I did. Had block bored, got crank checked and polished, had rods checked and new bolt installed and some forged flat tops put on.(think they were speedpro can't remember to good) standard rebuild stuff new rings & bearings (setting up bearing clearance) then for the heads, I took one of my regular sets of 1.94 heads and ported and polished them (I'm just lucky on the heads deal, cause I use to do that for a job for 4 yrs) I put stainless steel undercut valves in the heads along with brass guides, cut for PC seals and springs to match the cam and 3 angle valve job. (like I said I do all my own head work) What I'm trying to say here with the heads is I didn't spend big cash on aftermarket heads. Now for the cam I can't remember to good what the specs were exactly but I know it was a flat tappet hyd cam from Lunati adv. duration was around 276, but here the thing to remember to much and your at risk of reversion, and yes I still run stock manifolds but I have gotten away with it due to I modified the risers, I cheated and extended the exhaust pipe about 5"- 6" then it takes a turn into my S pipe because I have a swim platform. Intake I have a holley intake and I run a Rochester carb with the Thunder bolt IV ignition. So this is just my POOR mans way of hopping thing up with little bit of money. The boat ant pretty but it sounds DAMN good!! she be hit'n

Hey I know this combo ant glamorous but it works for me, OSO people on here are great!! and are a great resouce and probably have better ideas than me. Good Luck!!

jack, whaddya do with the risers? just extend the inside pipe a ways? sounds like a plan. i have 4 alum GLM's and they go straight into rubber hose out the thru hulls. heck, maybe i will add alum conduit and run 'em right out the thru hulls...lol.

yep, thats what I did, my manifolds are cast so it was easy for me to weld a piece of exhaust pipe onto the end of the inside exhaust pipe, I cut the end of the pipe about to a 45 degree or so, so that the water had even further to go before they met. I also have a S pipe so the exhaust gets dumped straight down anyway. This was the first time I have ever tried this it seemed to work, been running it for years this way, I got this idea from a friend in VA Beach VA. that told me about reversion and how I might try this back yard redneck style, but he did caution me, there is a limit to this trick which I'm sure there is, but what the limitations are I don't really know. I'm NO expert, I tried this crazy trick and it seemed to work for me, but I can't say it will work for the next guy and his cam set up, you'll have to be the judge of that. I tried drawing a picture of what I did. Hope this helps and good luck!!

I guess the right way would be to buy aftermarket stuff $$ But at the time I was being a cheap azz :lolhit:

If you are stuck on flat tappet...I have always had good luck with the Crane "Blueprint" copy of the 350 horse 350 hydraulic 'Vette~Z/28 cam from the 60's and early 70's. Makes a ton of TQ and will wind a 350 to 6000 RPM if you want to. Very good low end and good "dock manners"...it does however require the "best" push rods and springs to make the motor live. Run these cams in carefully...there is a "bunch" of pressure on the lobes so be liberal with the assembly lube that has zinc and molybdenum in it. Crane sends a tube of this with their Cam & lifter kits...USE IT!! I have seen this step by passed and have motors "making metal" in no time.

Sounds like a nice clean build...but seriously consider going to a roller. It will make things easier for just a few more $$$.